Bladder Volume Variation Research Articles

Study of variation of dose due to interfraction organ movement in interstitial brachytherapy: A single institute experience

Introduction: Concurrent chemo-radiation is the main treatment in locally advanced cervical cancer. The change of bladder and rectum volume may lead to change in the positions of these structures and target volume during MUPIT implant which may lead to variation in dose to the organ at risk and target. Materials and Methods: Ten patients of gynecological malignancy were included. MUPIT template was positioned under anesthesia. CT scan was done for the contouring of bladder, rectum, and target and for planning purpose which generates plan (P1). CT scan was repeated before the third fraction of the treatment (CT2). The resultant plan (P2) was analyzed qualitatively and quantitatively. Results: Bladder volume variations of 88.18% to -68.15% were noted. This change in volume lead to differences in the maximum dose in bladder between fractions. The maximum dose variation ranged from 62.53% to -21.49%. The rectal volume variation ranges 11.71% to -46.20% due to the rectal filling. High variation in maximum dose to the rectum were observed which might be due to rectal filling. CTV volume is increased by 19.48% while in other by 19.05% and in all other patients the volume is decreased. CTV volume maximum decreased by 30.54% which might be due to decrease in edema developed during procedure. The volume variation in CTV is in range of 19.48% to -30.54%. Conclusion: It is proposed that re-planning using repeat CT scan is required before third fraction implementation.

Evaluating Variations of Bladder Volume Using an Ultrasound Scanner in Rectal Cancer Patients during Chemoradiation: Is Protocol-Based Full Bladder Maintenance Using a Bladder Scanner Useful to Maintain the Bladder Volume?

PurposeThe maintenance of full bladder is important to reduce radiation-induced toxicities and maintain the therapeutic consistency in locally advanced rectal cancer patients who underwent radiotherapy (RT). So, the aim of this study was to evaluate the effectiveness of protocol-based full bladder maintenance by assessing bladder volume variation using an ultrasound bladder scanner to maintain bladder volume.Materials and MethodsFrom March 2011 to May 2011, twenty consecutive rectal cancer patients receiving external beam RT participated in this prospective study. Protocol-based full bladder maintenance consisted of education, training and continuous biofeedback by measuring bladder volume. Bladder volume was measured by bladder scan immediately before simulation CT scan and before each treatment three times weekly during the RT period. The relative bladder volume change was calculated. Intra-patient bladder volume variations were quantified using interquartile range (IQR) of relative bladder volume change in each patient. We compared intra-patient bladder volume variations obtained (n=20) with data from our previous study patients (n=20) performing self-controlled maintenance without protocol.ResultsBladder volumes measured by bladder scan highly correlated with those on simulation CT scan (R=0.87, p<0.001). Patients from this study showed lower median IQR of relative bladder volume change compared to patients of self-controlled maintenance from our previous study, although it was not statistically significant (median 32.56% vs. 42.19%, p=0.058). Upon logistic regression, the IQR of relative bladder volume change was significantly related to protocol-based maintenance [relative risk 1.045, 95% confidence intervals (CI) 1.004-1.087, p=0.033]. Protocol-based maintenance included significantly more patients with an IQR of relative bladder volume change less than 37% than self-controlled maintenance (p=0.025).ConclusionOur findings show that bladder volume could be maintained more consistently during RT by protocol-based management using a bladder scan.

The influence of the bowel and bladder preparation protocol for radiotherapy of prostate cancer using kilo-voltage cone beam CT: Our experience.

The purpose of this study is to determine the influence of bladder and bowel preparation protocols on the dose-volume histograms (DVHs) of these organs using the cone beam computed tomography (CBCT)-based intensity modulated radiotherapy (IMRT) treatment planning for prostate cancer patients. The pelvic DVHs of 12 prostate cancer patients were studied using CBCT images obtained immediately before each treatment. Six patients had bladder and bowel preparation protocol whilst the other six patients were the control group. Contoured bladder and rectal volumes on CBCT images were compared with planning computed tomography. All patients were treated with IMRT with 7800 cGy in 39 fractions over 8 weeks. Compared with the patient with bladder preparation protocol, patients without bladder preparation instruction had higher bladder volume and dose variation. The maximum variation in bladder volume was as high as 98% in the control group. Without bowel preparation protocol, the rectal volumes were more variability. Owing to changes in rectal filling on the day of treatment, the maximum variation in rectal volume was as high as + 96%. With bowel preparation protocol, the maximum rectum volume variations were less than 25%. The changes in prostate target dose compared with planning dose were minimal as would be expected from positioning with daily image guidance and gold seed implanted.

Inter- and intra-fractional bladder motion during radiotherapy for bladder cancer: A comparison of full and empty bladders

PurposeTo compare inter- and intra-fraction bladder volume variations and bladder wall motion during radiotherapy (RT) for bladder cancer with full and empty bladder protocols. Materials and methodsBladder volumes, filling rates and bladder wall movement were retrospectively analyzed for 24 patients with at least 4 sets of delineable pre and post treatment cone beam CT (CBCT)-scans. Eight patients were treated with an ‘empty bladder’ (EB) protocol and sixteen patients with a ‘full bladder’ (FB) protocol. Results24 planning CT-scans and 356 CBCT-scans (178 sets) were analyzed. The average time between pre and post irradiation CBCT was 8min (range 6–18min). Median filling rate was 1.94ml/min and did not differ between EB and FB. Random variation in bladder volume and inter-fraction wall movement was slightly but not significantly larger for FB, whereas intra-fraction bladder wall movement was slightly but not significantly smaller for FB. The largest inter- and intra-fraction bladder wall movement was found in the cranial anterior direction. ConclusionEmpty and full bladder protocols show similar inter- and intra-fraction wall motion, and therefore treatment choices could be purely based on organ at risk criteria.

Comparison study of portable bladder scanner versus cone‐beam CT scan for measuring bladder volumes in post‐prostatectomy patients undergoing radiotherapy

In post-prostatectomy radiotherapy to the prostatic bed, consistent bladder volume is essential to maintain the position of treatment target volume. We assessed the differences between bladder volume readings from a portable bladder scanner (BS-V) and those obtained from planning CT (CT-V) or cone-beam CT (CBCT-V). Interfraction bladder volume variation was also determined. BS-V was recorded before and after planning CT or CBCT. The percentage differences between the readings using the two imaging modalities, standard deviations and 95% confidence intervals were determined. Data were analysed for the whole patient cohort and separately for the older BladderScan™ BVI3000 and newer BVI9400 model. Interfraction bladder volume variation was determined from the percentage difference between the CT-V and CBCT-V. Treatment duration, incorporating the time needed for BS and CBCT, was recorded. Fourteen patients were enrolled, producing 133 data sets for analysis. BS-V was taken using the BVI9400 in four patients (43 data sets). The mean BS-V was 253.2 mL, and the mean CT-V or CBCT-V was 199 cm(3). The mean percentage difference between the two modalities was 19.7% (SD 42.2; 95%CI 12.4 to 26.9). The BVI9400 model produced more consistent readings, with a mean percentage difference of -6.2% (SD 27.8; 95% CI -14.7 to -2.4%). The mean percentage difference between CT-V and CBCT-V was 31.3% (range -48% to 199.4%). Treatment duration from time of first BS reading to CBCT was, on average, 12 min (range 6-27). The BS produces bladder volume readings of an average 19.7% difference from CT-V or CBCT-V and can potentially be used to screen for large interfraction bladder volume variations in radiotherapy to prostatic bed. The observed interfraction bladder volume variation suggests the need to improve bladder volume consistency. Incorporating the BS into practice is feasible.

A randomized trial comparing bladder volume consistency during fractionated prostate radiation therapy

PurposeOrgan motion is a contributory factor to the variation in location of the prostate and organs at risk during a course of fractionated prostate radiation therapy (RT). A prospective randomized controlled trial was designed with the primary endpoint to provide evidence-based bladder-filling instructions to achieve a consistent bladder volume (BV) and thus reduce the bladder-related organ motion. The secondary endpoints were to assess the incidence of acute and late genitourinary (GU) and gastrointestinal (GI) toxicity for patients and patients’ satisfaction with the bladder-filling instructions. Methods and materialsOne hundred ten patients were randomly assigned to 1 of 2 bladder-filling protocols; 540 mL (3 cups) of water or 1080 mL (6 cups) of water, in a single institution trial. A portable ultrasound device, BladderScan BVI 6400 (Verathon Inc, Bothell, WA), measured BVs at treatment planning computed tomography (TPCT) scan and 3 times per week during RT. Maximum bladder dose and BV receiving ≥ 50, 60, and 70 Gy were recorded. Acute and late GU and GI toxicity were evaluated, as were patients’ comfort, perception of urinary symptoms, and quality of life (QoL). ResultsThere was significantly less BV variation in the 540 mL arm when compared with 1080 mL (median: 76 mL vs 105 mL, P = .003). Larger BVs on initial TPCT correlated with larger BV variations during RT (P < .0005). There were no statistically significant associations between arm and GU/GI toxicity, dose median comfort scores, or median QoL scores. ConclusionsThe 540 mL bladder-filling arm resulted in reproducible BVs throughout a course of RT, without any deterioration in QoL or increase in toxicities for prostate patients.

Adaptive plan selection vs. re-optimisation in radiotherapy for bladder cancer: A dose accumulation comparison

PurposePatients with urinary bladder cancer are obvious candidates for adaptive radiotherapy (ART) due to large inter-fractional variation in bladder volumes. In this study we have compared the normal tissue sparing potential of two ART strategies: daily plan selection (PlanSelect) and daily plan re-optimisation (ReOpt). Materials and methodsSeven patients with bladder cancer were included in the study. For the PlanSelect strategy, a patient-specific library of three plans was generated, and the most suitable plan based on the pre-treatment cone beam CT (CBCT) was selected. For the daily ReOpt strategy, plans were re-optimised based on the CBCT from each daily fraction. Bladder contours were propagated to the CBCT scan using deformable image registration (DIR). Accumulated dose distributions for the ART strategies as well as the non-adaptive RT were calculated. ResultsA considerable sparing of normal tissue was achieved with both ART approaches, with ReOpt being the superior technique. Compared to non-adaptive RT, the volume receiving more than 57Gy (corresponding to 95% of the prescribed dose) was reduced to 66% (range 48–100%) for PlanSelect and to 41% (range 33–50%) for ReOpt. ConclusionThis study demonstrated a considerable normal tissue sparing potential of ART for bladder irradiation, with clearly superior results by daily adaptive re-optimisation.

Daily Variation in Bladder and Rectal Volume During Postoperative Whole Pelvic Intensity Modulated Radiation Therapy

Daily Variation in Bladder and Rectal Volume During Postoperative Whole Pelvic Intensity Modulated Radiation Therapy

Implementation of adaptive radiation therapy for urinary bladder carcinoma: Imaging, planning and image guidance

Background. Adaptive radiation therapy (ART) for urinary bladder cancer has emerged as a promising alternative to conventional RT with potential to minimize radiation-induced toxicity to healthy tissues. In this work we have studied bladder volume variations and their effect on healthy bladder dose sparing and intrafractional margins, in order to refine our ART strategy. Material and methods. An online ART treatment strategy was followed for five patients with urinary bladder cancer with the tumors demarcated using Lipiodol®. A library of 3–4 predefined treatment plans for each patient was created based on four successive computed tomography (CT) scans. Cone beam CT (CBCT) images were acquired before each treatment fraction and after the treatment at least weekly. In partial bladder treatment the sparing of the healthy part of the bladder was investigated. The bladder wall displacements due to bladder filling were determined in three orthogonal directions (CC, AP, DEX-SIN) using the treatment planning CT scans. An ellipsoidal model was applied in order to find the theoretical maximum values for the bladder wall displacements. Moreover, the actual bladder filling rate during treatment was evaluated using the CBCT images. Results. In partial bladder treatment the volume of the bladder receiving high absorbed doses was generally smaller with a full than empty bladder. The estimation of the bladder volume and the upper limit for the intrafractional movement of the bladder wall could be represented with an ellipsoidal model with a reasonable accuracy. Observed maximum growth of bladder dimensions was less than 10 mm in all three orthogonal directions during 15 minute interval. Conclusion. The use of Lipiodol contrast agent enables partial bladder treatment with reduced irradiation of the healthy bladder volume. The ellipsoidal bladder model can be used for the estimation of the bladder volume changes and the upper limit of the bladder wall movement during the treatment fraction.

SU‐E‐J‐146: Effectiveness of Daily Endorectal Balloon for Post‐Prostatectomy Patients Undergoing Pencil Beam Scanning Proton Therapy

Purpose: Pencil beam scanning proton therapy was found more sensitive to organ motion as compared to conventional IMRT. Significant target under dose may be caused by interfractional tumor motion. The objectives of this study are to investigate the role of endorectal balloon (ERB) in daily patient setup throughout the course of proton therapy and its dosimetric impact. Methods: Ten consecutive post‐prostatectomy patients enrolled on a prospective IRB approved institutional study were analyzed. Patients underwent CT/MRI simulation and treatment with daily ERB. Six T2‐MRI verification scans were performed during the treatment course. A pencil beam scanning proton therapy plan was generated for each patient. Organ at risks and CTVs were contoured by physician on each of the weekly MRI scans. The MRI scans were subsequently rigidly fused to the CT simulation images in order to simulate 2 possible daily kV‐kV patient setups: 1) alignment to bony anatomy and 2) alignment to pelvic bone in cranial caudal direction and ERB along the AP and lateral direction. The dosimetric impact of interfraction target motion on target coverage was compared for both scenarios. Results: We found that target interfraction motion in the AP direction (average 4.1mm) is consistently larger than those in the lateral and cranial caudal directions (2.9 mm and 3mm respectively) most likely due to variations in bladder volume. ERB can be used to further improve the patient bony alignment(∼1mm), in AP and lateral directions. Overall when both ERB pelvic bony structures are used for patient alignment, we observed a median 4.03% decrease in V98% of CTV as compared to 8.27% when only bony alignment is used. Conclusion: In post‐prostatectomy patients undergoing pencil beam scanning proton therapy, daily patient setup via bony alignment and ERB can stabilize the target and maintain the dose coverage within 5% relative to the initial treatment plans.

Quantifying daily variation in volume and dose to the prostate, rectum and bladder using cone-beam computerised tomography

AbstractIntroductionIn the era of dose escalation for localised prostate cancer, the dose–volume histogram (DVH) is integral to the assessment of rectum and bladder dose constraints. However, reliance on a single planning computerised tomography-based (P-CT) dose distribution may not account for variations in delivered dose that results from deformation of the prostate, bladder and rectum. This study uses cone-beam CT (CBCT) datasets from five patients to investigate the concordance between the dose prediction from the initial treatment plan and the dose delivered during treatment.MethodsThe intensity-modulated radiation therapy distribution used for treatment was superimposed on alternate day CBCT images for each patient. Dose metrics and absolute volumes for the prostate, rectum and bladder were extracted from the CBCT-based DVH. Differences in dose and volumes were compared with the P-CT values, and significance was tested using the Wilcoxon signed-rank test.ResultsFor all five case studies, the prostate dose coverage on CBCT plans was lower than predicted with an average reduction of 3% in mean dose. Significant differences in rectal volumes and dose were observed in two out of five and four out of five patients, respectively. Reductions in bladder volume and subsequent increases in dose were observed for three out of five patients.ConclusionThe DVH from P-CT was unable to consistently predict the dose delivered to the bladder and rectum. The current bowel and bladder preparation protocols used at our institution did not eliminate variation in bladder and rectum volumes for the five patients included in this study.

OC-0359: Bladder volume variation reduces long-term toxicity of imageguided brachytherapy for cervical cancer

OC-0359: Bladder volume variation reduces long-term toxicity of imageguided brachytherapy for cervical cancer

Degradation of target coverage due to inter-fraction motion during intensity-modulated proton therapy of prostate and elective targets

Internal target and organ motion during treatment is a challenge in radiotherapy (RT) of the prostate and the involved elective targets, with residual motion being present also following image-guidance strategies. The aim of this study was to investigate organ motion-induced dose degradations for the prostate, seminal vesicle and the pelvic lymph node when treating these targets with proton therapy, using different image-guidance and delivery strategies. Material and methods. Four patients were selected from a larger series as they displayed large inter-fractional variation in bladder and rectum volume. Intensity-modulated proton therapy plans were generated using both simultaneous integrated and sequential boost delivery. For each technique, three isotropic margin expansions (in the range of 4–10 mm) were evaluated for the clinical target volume of prostate (CTV-p), seminal vesicles (CTV-sv) and lymph nodes (CTV-ln). Simulation of the dose degradations for all treatment plans were based on dose re-calculations for the 8–9 repeat CTs available for each patient, after applying rigid registrations to reproduce set-up based on either intra-prostatic fiducials or bony anatomy. Results. The simulated dose received by 99% of the target volume (D99) and generalized equivalent dose (gEUD) showed substantial inter-patient variations. For 40% of the investigated scenarios, the patient average simulated D99 for all targets were within 2 GyE from the planned dose. The largest difference between simulated and planned dose was seen for the CTV-sv when using SIB delivery, with an average relative reduction in D99 of 13% and 15% for the largest margin expansion, when positioned using fiducials and bony anatomy, respectively. Conclusions. The most severe dose degradations were found for CTV-sv, but they were also evident for CTV-ln. The degradations could not be completely resolved, neither by using the largest margin expansion nor with the choice of set-up. With fiducial set-up CTV-p was robust against the inter-fraction changes.

Bladder filling variations during concurrent chemotherapy and pelvic radiotherapy in rectal cancer patients: early experience of bladder volume assessment using ultrasound scanner

PurposeTo describe the early experience of analyzing variations and time trends in bladder volume of the rectal cancer patients who received bladder ultrasound scan.Materials and MethodsWe identified 20 consecutive rectal cancer patients who received whole pelvic radiotherapy (RT) and bladder ultrasound scan between February and April 2012. Before simulation and during the entire course of treatment, patients were scanned with portable automated ultrasonic bladder scanner, 5 times consecutively, and the median value was reported. Then a radiation oncologist contoured the bladder inner wall shown on simulation computed tomography (CT) and calculated its volume.ResultsBefore simulation, the median bladder volume measured using simulation CT and bladder ultrasound scan was 427 mL (range, 74 to 1,172 mL) and 417 mL (range, 147 to 1,245 mL), respectively. There was strong linear correlation (R = 0.93, p < 0.001) between the two results. During the course of treatment, there were wide variations in the bladder volume and every time, measurements were below the baseline with statistical significance (12/16). At 6 weeks after RT, the median volume was reduced by 59.3% to 175 mL. Compared to the baseline, bladder volume was reduced by 38% or 161 mL on average every week for 6 weeks.ConclusionTo our knowledge, this study is the first to prove that there are bladder volume variations and a reduction in bladder volume in rectal cancer patients. Moreover, our results will serve as the basis for implementation of bladder training to patients receiving RT with full bladder.

Bladder dose accumulation based on a biomechanical deformable image registration algorithm in volumetric modulated arc therapy for prostate cancer

Variations in bladder position, shape and volume cause uncertainties in the doses delivered to this organ during a course of radiotherapy for pelvic tumors. The purpose of this study was to evaluate the potential of dose accumulation based on repeat imaging and deformable image registration (DIR) to improve the accuracy of bladder dose assessment. For each of nine prostate cancer patients, the initial treatment plan was re-calculated on eight to nine repeat computed tomography (CT) scans. The planned bladder dose–volume histogram (DVH) parameters were compared to corresponding parameters derived from DIR-based accumulations as well as DVH summation based on dose re-calculations. It was found that the deviations between the DIR-based accumulations and the planned treatment were substantial and ranged (−0.5–2.3) Gy and (−9.4–13.5) Gy for D2% and Dmean, respectively, whereas the deviations between DIR-based accumulations and DVH summation were small and well within 1 Gy. For the investigated treatment scenario, DIR-based bladder dose accumulation did not result in substantial improvement of dose estimation as compared to the straightforward DVH summation. Large variations were found in individual patients between the doses from the initial treatment plan and the accumulated bladder doses. Hence, the use of repeat imaging has a potential for improved accuracy in treatment dose reporting.

Patient-Specific PTV Margins and Their Implementation in Radiation Therapy for Bladder Cancer

Background: Precision during bladder cancer radiotherapy delivery is particularly challenging due to large daily variations in bladder position and volume. The literature suggests that the optimal approach to margin calculation is a patient-specific one, because the magnitude and direction of bladder changes varies significantly between patients. There is considerable inconsistency in the strategies used to calculate a patient-specific planning target volume (psPTV), with authors reporting the use of data from 1 to 15 with a pattern of daily to weekly fractions. Therefore, the purpose of this study is to determine the optimal number and pattern of data points to be used to generate psPTV margins and to determine if implementing those margins at the earliest opportunity would result in a reduction in organ at risk (OAR) dose. Methods and Materials: This is a secondary analysis of a prospective clinical trial. All patients provided informed consent prior to participation in the clinical trial. Of the 30 patients accrued to the clinical trial, a sample of 15 (selected reverse chronologically) will be included in this secondary analysis. These patients received 46Gy in 23f to the whole pelvis and 20Gy in 10f to the bladder or partial bladder. Daily kV conebeam CTs (CBCT) were acquired for image guidance purposes. Local current practice requires bladder contours from the first 15 daily CBCT to generate a psPTV for implementation in the phase 2 treatment. This current practice will be used as a gold standard (GS) against which various experimental strategies (ES) will be compared, such as ‘‘first five daily fractions,’’ four weekly fractions, etc. Differences between the psPTV generated using GS versus all ES will be quantified using the following study metrics: volume, superior margin, posterior margin and clinical target volume (CTV) coverage. Once the optimal margin generation strategy is identified, the psPTV will be incorporated into the treatment plan for the remaining number of fractions. Rectal and small bowel dose volume histograms will be used to quantify any differences between the strategies. Results: Although data collection is not yet complete, based on this research design and the findings from similar evaluations for other pelvic organs, we hypothesize that it will be possible to generate psPTV margins with data from less than 15 daily fractions. This would allow an earlier adoption of the psPTV margin, which could reduce doses to the small bowel and rectum. Alternatively, if our findings suggest that 15 daily data points are necessary to generate an adequate psPTV, this would support our current practice as the optimal method. Conclusions: Precision radiation therapy for bladder cancer is technically challenging. A patient-specific approach to PTV margins is clearly necessary, but there is little evidence to guide the practitioner when designing such margin generation strategies. With this study we hope to establish an optimal regimen for generating psPTV that will result in excellent CTV coverage, but the lowest possible doses to the adjacent OARs.

Patient-specific PTV margins in radiotherapy for bladder cancer – A feasibility study using cone beam CT

Purpose To assess the feasibility of using cone beam computed tomography (CBCT) to generate patient-specific PTV margins for bladder cancer patients treated with radiation therapy (RT). Methods Eleven patients underwent CT simulation and daily RT (full bladder and empty rectum). CBCT was done prior to each fraction, and the whole bladder was contoured off-line. For the first 15 CBCTs of each patient, the bladder was aligned with CT-simulation bladder (pBladder) to create an occupancy volume (OV). A 5 mm isotropic margin was added to OV (OV + 5). A measurement-based PTV (mPTV) was generated by measuring maximal displacement between pBladder and OV in six directions. OV, OV + 5, mPTV, and a standard PTV (2 cm isotropic margin) were compared for absolute and relative volume differences. Using the final 10 CBCT of each patient, the ability of each study volume to encompass the entire CBCT bladder was determined. Results 161/165 CBCT images were of adequate quality for contouring. No daily trend in bladder volume variation was noted. The median absolute volumes (cm 3) were: 221, 271, 426, 440, and 914 for pBladder, OV, OV + 5, mPTV, and standard PTV, respectively. The median ratios of the study volumes/pBladder were: 1.4 OV, 2.1 OV + 5, 2.4 mPTV, 4.1 standard PTV. OV + 5 was smaller than mPTV in 9 patients. There was considerable inter-patient variability in study volumes and no apparent association of the magnitude of margin expansion and pBladder. The bladder was encompassed in 69%, 99%, 99%, and 100% of the final 10 fractions by OV, OV + 5, mPTV, and standard PTV, respectively. Conclusions The use of daily CBCT to generate patient-specific PTV margins is feasible and results in a marked reduction in the irradiated volume compared to population-based margins. As daily bladder volume varied unpredictably with considerable differences between patients, these findings support the use of patient-specific PTV margin expansions for bladder radiotherapy.

Dosimetric uncertainties related to the elasticity of bladder and rectal walls: Adenocarcinoma of the prostate

Purpose Radiotherapy is an important treatment for prostate cancer. During treatment sessions, bladder and rectal repletion is difficult to quantify and cannot be measured with a single and initial CT scan acquisition. Some methods, such as image-guided radiation therapy and dose-guided radiation therapy, aim to compensate this missing information through periodic CT acquisitions. The aim is to adapt patient's position, beam configuration or prescribed dose for a dosimetric compliance. Methods We evaluated organ motion (and repletion) for 54 patients after having computed the original ballistic on a new CT scan acquisition. A new delineation was done on the prostate, bladder and rectum to determine the new displacements and define organ doses mistakes (equivalent uniform dose, average dose and dose–volume histograms). Results The new CT acquisitions confirmed that bladder and rectal volumes were not constant during sessions. Some cases showed that previously validated treatment plan became unsuitable. A proposed solution is to correct dosimetries when bladder volume modifications are significant. The result is an improvement for the stability of bladder doses, D50 error is reduced by 25.3%, mean dose error by 5.1% and equivalent uniform dose error by 2.6%. For the rectum this method decreases errors by only 1%. This process can reduce the risk of mismatch between the initial scan and following treatment sessions. Conclusion For the proposed method, the cone-beam CT is necessary to properly position the isocenter and to quantify bladder and rectal volume variation and deposited doses. The dosimetries are performed in the event that bladder (or rectum) volume modification limits are exceeded. To identify these limits, we have calculated that a tolerance of 10% for the equivalent uniform dose (compared to the initial value of the first dosimetry), this represents 11% of obsolete dosimetries for the bladder, and 4% for the rectum.

Vaginal Motion and Bladder and Rectal Volumes During Pelvic Intensity-Modulated Radiation Therapy After Hysterectomy

To evaluate variations in bladder and rectal volume and the position of the vaginal vault during a 5-week course of pelvic intensity-modulated radiation therapy (IMRT) after hysterectomy. Twenty-four patients were instructed how to fill their bladders before simulation and treatment. These patients underwent computed tomography simulations with full and empty bladders and then underwent rescanning twice weekly during IMRT; patients were asked to have full bladder for treatment. Bladder and rectal volumes and the positions of vaginal fiducial markers were determined, and changes in volume and position were calculated. The mean full and empty bladder volumes at simulation were 480 cc (range, 122-1,052) and 155 cc (range, 49-371), respectively. Bladder volumes varied widely during IMRT: the median difference between the maximum and minimum volumes was 247 cc (range, 96-585). Variations in rectal volume during IMRT were less pronounced. For the 16 patients with vaginal fiducial markers in place throughout IMRT, the median maximum movement of the markers during IMRT was 0.59 cm in the right-left direction (range, 0-0.9), 1.46 cm in the anterior-posterior direction (range, 0.8-2.79), and 1.2 cm in the superior-inferior direction (range, 0.6-2.1). Large variations in rectal or bladder volume frequently correlated with significant displacement of the vaginal apex. Although treatment with a full bladder is usually preferred because of greater sparing of small bowel, our data demonstrate that even with detailed instruction, patients are unable to maintain consistent bladder filling. Variations in organ position during IMRT can result in marked changes in the position of the target volume and the volume of small bowel exposed to high doses of radiation.

Variability in Bladder Volumes of Full Bladders in Definitive Radiotherapy for Cases of Localized Prostate Cancer

To evaluate variation in bladder volume of full bladders in definitive radiotherapy for localized prostate cancer and to investigate potential predictors of increased bladder volume variations. In 40 patients, the bladder volume was measured with megavoltage computed tomography (MVCT) imaging performed just before irradiation during the administration of the 1st fraction (#1), the 10th fraction (#10), the 20th fraction (#20), and the 30th fraction (#30). Patients were instructed to avoid urinating for 60-90 minutes before the planning CT (pln-CT) scan and before daily irradiation. Patients were also encouraged to drink an unspecified volume of liquid that would result in a clear but tolerable urge to urinate. The population-mean bladder volume (±1SD) was 219 ml (±83 ml) at the planning CT scan (pln-CT), 186 ml (±96 ml) at #1, 149 ml (±73 ml) at #10, 137 ml (±59 ml) at #20, and 136 ml (±60 ml) at #30. The mean intrapatient variation in bladder volume (1 SD relative to the mean bladder volume of each patient) was 38% (range: 10-84%). The bladder volume at the pln-CT was correlated with the intrapatient variance in bladder volume with a correlation coefficient of 0.54 and p <0.001. We observed a significant decline in bladder volumes during the course of radiotherapy. The bladder volume at the pln-CT was a significant predictor of increased bladder volume variations.